Electrolytes for electrolytic condensers



United States Patent ELECTROLYTES FOR ELECTROLYTIC CONDENSERS Hans Schulz, Walter Bludau, and Joachim Lesche, Gem, and Erika Bottcher, Ronneburg, Germany, assimiors to VEB Kondensatorenwerk Gera, Gera, Germany No Drawing. Filed May 15, 1957, Ser. No. 659,394 Claims priority, application Germany May 26, 1956 2 Claims. (Cl. 252-622) This invention relates to condensers and more particularly to electrolytic condensers and electrolytes for use in electrolytic condensers.

The invention is particularly concerned with novel electrolytes and their production, which electrolytes are suitable for use in electrolytic condensers adapted to function within a temperature range of about 70 C to +90 C.

Known electrolytes used in electrolytic condensers generally consist of weak acids, particularly boric acid, salts of such acids and certain alcohols, preferably glycol or glycerol. These components are subjected to a boiling treatment resulting in partial esterification. Further, due to the boiling treatment, the partially esterified mixture becomes more viscous since the water originally contained in the mixture as well as the water formed by the esterification evaporates dependent on the boiling temperature employed. Electrolytes obtained in this manner cannot be employed in electrolytic condensers, adapted to function at low temperatures, since the electrolytes become too viscous and even may crystallize, whereby the conductivity of the electrolytes drops below the required minimum and the electrolyte may chemically attack the electrode material used in the condenser, thus creating possibility of corrosion.

With a view to avoiding these disadvantages various measures have been attempted and adopted, none of which, however, has been entirely successful. These measures were designed to increase the conductivity of the electrolyte to the desired value and to eliminate danger of corrosion at low temperatures. By diluting the electrolytes with certain selected solvents it has, for example, been rendered possible to broaden the temperature range at which the condensers will function satisfactorily. The use of such selected solvents causes a lowering of the lower temperature limit of the range to about -40 C.; on the other hand, however, the presence of such solvents affects the upper temperature limit of the range owing to the increased vapor pressure of these solvents.

Further, when the temperature drops to below about C., an abrupt diminution of capacitance sets in, which renders it difiicult to comply with the DIN (German Standard Specifications) requirements concerning the permissible values of capacitance diminution at temperatures of 40 C. Analogously, the residual current and thus the loss factor (phase angle difference) is increased considerably with decreasing temperature.

It is an object of this invention to provide electrolytes for use in electrolytic condensers which electrolytes overcome the aforementioned drawbacks of known electrolytes, whereby a faultless and etlicient operation for electrolytic condensers is rendered possible at very low temperatures.

The novel electrolytes of the present invention comprise (1) an electrolytic substance or composition and (2) a solvent for diluting the electrolytic substance or composition. The solvent must fulfill all of the following requirements:

(a) The solvent must have a boiling point of C. and a solidification point of at least --70 C. (and preferably still lower).

(b) The solvent must be of hydrophilic nature, i.e. miscible with water in the desired ratio.

(c) Neither the solvent proper nor its conversion products should have a damaging or decomposing effect on the electrolytic substance or composition or on the elements of the condenser.

In accordance with this invention it has been ascertained that certain unsaturated alcohols fulfill all these requirements, and the allyl alcohol has been found to be particularly suitable for the inventive purpose, i.e. for diluting the electrolytic substance or composition.

The electrolytic substance or composition to be used in the inventive electrolyte may be of customary nature, i.e. for example boric acid and glycol may be used.

The inventive electrolytes will now be illustrated by an example, it being understood, however, that this example is given by way of illustration rather than by way of limitation and that many changes may be made in, for example, quantity relations and choice of raw materials without departing in any way from the scope of the invention as recited in the appended claims.

Example Crystalline boric acid is mixed with glycol in a weight ratio of 1:2, whereafter concentrated ammonia is added to the mixture thus obtained until a pH value of 6.0 is obtained. The mixture is then heated to a temperature of about l30l35 C. After cooling, the mixture is dissolved in twice the amount (by weight) of allyl alcohol. The solution or electrolyte thus obtained exhibited the following conductivity values:

At +30 C. about 1900 ,us./cm., At ---40 C. about 63 s./cm., and At 60 C. about 10 rs/cm.

The sparking voltage or potential of the electrolyte amounts to about 470-500 v. measured on smooth aluminum electrodes. Electrolytic condensers (6/8 v., smooth foil) which are manufactured with above electrolyte exhibited at a temperature of -40 C. a capacitance diminution or drop of about 22% as compared to the capacity at room temperature. (According to German Standard Specifications a capacitance diminution of 50% is permissible.) The loss factor (phase angle difference) of such a condenser had a value of about 0.4-0.5, which constitutes a very satisfying result. If the electrolyte is used in the manufacture of high-voltage condensers considerable more favorable values are obtained.

An electrolytic condenser, comprising an electrolyte prepared in accordance with this example, was subjected to continuous tests for a long period under changing temperature conditions. At the completion of the tests no corrosion of the elements of the condenser could be observed. Further, the condenser was stored for an extended period in the absence of current without the occurrence of corrosion phenomena.

Further, allyl alcohol may be successfully used without or in conjunction with other customary solvents normal- 1y employed in electrolytes. It has been ascertained that for example the following weight ratios of allyl alcohol to customary solvent may be chosen to yield mixtures which in conjunction with the electrolytic substance yield excellent electrolytes.

1) Allyl alcohol and ethyl glycol in a weight ratio of 1:1.

(2) Allyl alcohol and ethyl diglycol in a weight ratio of 2: 1.

(3) Allyl alcohol and ethyl alcohol in a weight ratio of 1:2.

The solvent mixtures thus obtained may in turn be supplied to the electrolytic substance, for example boric acid, in a weight ratio of 0.5: 1, 1:1 or 2: 1.

Further, allyl alcohol may be mixed with other suitable non-aqueous solvents.

The invention is not restricted to the use of the inventive solvent allyl alcohol in conjunction with glycol, glycerol, ethyl alcohol and the like.

During operation of electrolytic condensers, the stream or current of ions causes under certain circumstances chemical changes in the electrolyte. Primarily, oxidation phenomena may be expected on the anode of the condenser. If the hitherto customary solvents are used in the electrolyte, i.e. for example the common alcohols, glycol or the like, then the oxidation mechanism may readily cause the formation of fatty acids, which latter in turn are inclined to enhance corrosion of the condenser elements. However, the oxidation of unsaturated alcohols, particularly of allyl alcohol, as used in accordance with this invention, results under the influence of the anode potential, first in a splitting of the double bond of the alcohol, whereby for example, first saturated multivalent alcohols are formed, which latter do not possess corrosion-causing characteristics. It will be readily realized that this constitutes a very important advantage as compared to the employment of conventional electrolyte-solvents.

Allyl alcohol possesses a certain toxicity which should not be neglected and thus has to be considered in the manufacture of electrolytic condensers comprising the novel electrolytes.

We have described and shown preferred embodiments of our invention. However, it should be clearly understood that this disclosure is given by way of illustration rather than by way of limitation and that many alterations may be efiected without departing from the spirit and scope of this invention as recited in the appended claims.

What we claim is:

1. Electrolyte solution for use in an electrolytic condenser which comprises as major constituents a mixture of boric acid and glycol, in a weight ratio of about 1:2, which has been adjusted to a pH value of about 6 with ammonia and thereafter partially esterified by heating, and allyl alcohol as a solvent in an amount sufficient to impart to said electrolyte solution temperature stability in the range between C. and C.

2. Electrolyte solution for use in an electrolytic condenser which comprises a major amount of boric acid and allyl alcohol. as a solvent capable of imparting to said electrolyte solution temperature stability in the range between 40 C. and +70 C., said boric acid being in a weight ratio to said allyl alcohol of 0.5:1 to 2:1.

References Cited in the file of this patent UNITED STATES PATENTS 929,371 Arsem "a July 27, 1909 946,040 Hayden Jan. 11, 1910 1,924,435 Homer Aug. 29, 1933 1,973,602 Bergstein Sept. 11, 1934 2,085,958 Curtis July 6, 1937 2,668,225 Livingston Feb. 2, 1954 2,701,392 Eich Feb. 8, 1955 2,759,132 Ross Aug. 14, 1956 OTHER REFERENCES Handbook of Chem. and Physics, 34th ed., 1952-1953, Chem. Rubber Pub. Co., page 696. 

2. ELECTROLYTE SOLUTION FOR USE IN AN ELECTROLYTIC CONDENSER WHICH COMPRISES A MAJOR AMOUNT OF BORIC ACID AND ALLYL ALCOHOL AS A SOLVENT CAPABLE OF IMPARTING TO SAID ELECTROLYTE SOLUTION TEMPERATURE STABILITY IN THE RANGE BETWEEN -40*C. AND +70*C., SAID BORIC ACID BEING IN A WEIGHT RATIO TO SAID ALLYL ALCOHOL OF 0.5:1 TO 2:1. 